This invention relates to a silent chain power transmission device and, in particular, it relates to a silent chain, or inverted tooth chain, having a plurality of rows of links. The links are interleaved and connected by a connecting pin inserted in the apertures of each of the link plates. In its preferred embodiment, the chain links have teeth with convex outer flanks for seating with the teeth of the corresponding sprocket that is used with the silent chain.
Silent chains are used conventionally as power transmission chains for automobiles and motorcycles in engine timing systems as well as in transmissions and transfer cases for four-wheel drive vehicles. In general, a silent chain is comprised of multiple link plates, each of which has a pair of teeth. Each link typically includes a pair of apertures. The links are interleaved or connected by connecting pins placed in the link apertures.
FIG. 8 shows an example of a link plate of a conventional silent chain. In FIG. 8, link plate 100 has a pair of apertures or pinholes 101, 102 for insertion of the connecting pins and a pair of depending or downwardly extending teeth 103, 104 that engage with the teeth a sprocket (not shown). The teeth are joined at crotch area 105, which is formed of the inside link flanks. Tooth 103 includes inside flank 105a and outside flank 106 and tooth 104 is composed of inside flank 105b and outside flank 107.
When the silent chain comprised of multiples of links such as link plate 100 is operated, tension acts along the entire length of the chain. Thus, pressure from the connecting pins, in the direction to expand the pinhole center distance (or pitch) C, acts on pinholes 101, 102 of link plate 100.
As a result, cracks or breakage can occur in region A (or A') where the distance between the edge of pinhole 101 (or 102) and outside flank 106 (or 107) is the smallest. Therefore, as shown by the double dotted line in FIG. 8, the distance between the pinhole edge and the outside flank is conventionally made larger by placing outside flanks 106, 107 more toward the outside than conventional outside flanks 106, 107, shown by a solid line, for increasing the strength of the link plate in regions A, and A' in the prior art construction.
However, in this case, although the strength of the link plate increases, the thickness of the sprocket that engages with outside flanks 106, 107 of link plate 100 is typically correspondingly decreased. As a result, the strength of the sprocket teeth decreases.
The assignee of the present application has proposed a silent chain that can increase the strength of the link plate without decreasing the strength of the sprocket teeth and address such conventional problems, which is set forth in U.S. patent application Ser. No. 09/204,034, filed Dec. 1, 1998, the subject matter of which is incorporated herein by reference.
In that prior application, a protrusion is formed only in regions A, A' on the outside flank, and not along the entire link flank. Therefore, the strength and thickness of the sprocket teeth are ensured without decreasing the strength of the teeth and the strength of regions A, A' and the entire link plate is improved.
However, in the case of a silent chain of inside flank engagement (or crotch engagement) and outside flank seating (or outer-crotch seating), the inside flank (inner crotch) of the link plate of a certain link row engages first with the sprocket tooth and the point of engagement transfers on the inside flank along the progression of engagement.
When engagement with the sprocket tooth progresses further, the sprocket tooth engagement point on the inside flank of the link transfers onto the outside flank (outer crotch) of the link plate of the link row which is adjacent to the first link row, and, when engagement progresses, it moves along the outside flank and the engagement ends at a certain point. This final point is the seating point.
In the development of the chain of the present invention, the engagement mechanism of the silent chain of the conventional inner flank engagement followed by outer flank seating was analyzed in detail. The analysis showed that the transfer of load from the inside flank to the outside flank is not smooth during transfer of the engagement point from the inside flank to the outside flank because of the distance between the point of the end of engagement on the inside flank and the point of the start of engagement on the outside flank (i.e. engagement transfer point). Noise is generated as a result of the lack of smooth transfer.
Accordingly, the noise vibration performance of the silent chain (i.e., noise-vibration properties) is thought to be improved if the transfer of load during the engagement can be made smoothly. The present invention addresses such a problem and its purpose is to offer a silent chain power transmission device that improves the strength of the link plate of a silent chain without decreasing the strength of the sprocket teeth, making transfer of engagement from the inside flank to the outside flank smoother, thereby improving noise/vibration of the silent chain.